Looking for a short story about a 'transhuman' clandestine operative

Question

Looking for a short story about a seemingly superhuman person on a clandestine mission. We find out that he isn’t a superhuman but is well-trained and conditioned to perform the mission; he can see in the dark, can read minds (but this is his ability to hear sub-vocalized thoughts) along with great speed and agility. At the end of the story we are told that he will spend a long time recuperating from the mission as he is burnt out physically and mentally. Read in the 80’s in a short story collection. That’s all I remember.

Answer 1

Thanks to NomadMaker identifying the author as Poul Anderson, I believe that a strong candidate for an answer is the novella "The Sensitive Man", first published in 1954 in Fantastic Universe.

The story takes place in the far-future year of 2009(!), and is set in Poul's "Psychotechnic League" future history. A summary at wikipedia describes the plot well:

Michael Tighe of the Psychotechnic Institute has been kidnapped by Thomas Bancroft, a politician with ties to an authoritarian movement called the Actionists. Tighe's adopted son, Simon Delgatty, sets out to find him, but is himself captured by Bancroft and taken to his base on an island off the coast of Mexico. In the course of raising Delgatty, Tighe has trained him to exert conscious control over what are normally subconscious and autonomic brain functions. This allows Delgatty to speed up or slow down his metabolism at will, and also allows him to tell what other people are thinking by listening to them subvocalize their thoughts.

As the question noted, the protagonist, Delgatty,was trained to take advantage of "the relationship between the conscious, subconscious and involuntary minds" to have a perfect memory, have superhuman physical abilities, and to apparently read people's minds. In fact, however this is due to:

Most people sub-vocalize their surface thoughts. With a little practice a person who can hear those vibrations can learn to interpret them.

His abilities take a toll on his body though.

"There are sound biological reasons why man's mind is so divided and plenty of penalties attached to a case like mine. It'll take me a couple of months to get back in shape after this bout. I'm due for a good old-fashioned nervous breakdown and while it won't last long it won't be much fun while it does last."

The complete story is available at Project Gutenberg.